John thomas dempster



.(No Model.)

J. T. 'DBMPSTER.

ELECTRIC ARC LAMP.

No. 501,768. Patented July 18, 1893.

UNITED STATES PATENT OFFICE.

JOHN THOMAS DEMPSTER, OF SUMMIT, NEW JERSEY, ASSIGNOR TO SIGIWIUND BERGMANN, OF NEW YORK, N. Y.

ELECTRIC-ARC LAM P.

SPECIFICATION forming part of Letters Patent No. 501,768, dated July 18, 1893.

Application filed February 13, 1893- Serial No. 462,049. (No model.)

To all whom it may concern:

Be it known that I, JOHN THOMAS DEMP- STER, a subject of the Queen of Great Britain, and a resident of Summit, State of New Jersey, have invented certain new and useful Improvementsin Electric-Arc Lamps,of which the following is a specification.

My invention relates to electric arc lamps, and the object of my invention is to provide automatic means for switching the shunt electro-magnets out of the circuit after the carbons have ceased burning, thus economizing current. I accomplish this object by the means hereinafter described and set forth in the claims.

In the accompanying drawings forming part of this specification Figure 1 is a side elevation of an electric arc lamp mechanism embodying my invention. Fig. 2 is a plan view of the same, and Fig. 3 is a diagrammatic View showing the circuits.

In the drawings 1 represents the frame of an arc lamp, 2 the usual shunt magnets and 3 the rack bar which carries the upper car- 2 5 bon holder. On the insulating plate 4 is loosely pivoted a switch lever 5, (see Fig. 1) so that its free end is capable of a vertical as well as lateral motion. The free end of this switch lever makes electrical contact with the 0 rack bar while its opposite end is electrically connected by conductor 6 with the shunt electro-magnets. The said switch lever is kept in electrical contact with the rack bar by means of a spring 7 which also serves another 3 5 purpose as will presently appear. The rack bar is provided with a pyramidal top 8 capped with a cap 9 both constructed of insulating material. This insulating top and cap may be termed an insulating block.

The operation of the mechanism is as follows: The general switch 10 (see Fig. 3) being closed the lamp is in circuit and the upper carbon is fed downward as the carbons are consumed. About the time the carbons cease burning 5 the rack bar has descended sufficiently so that its insulating block is on a line with the switch lever. The moment the switch lever touches the inclined insulating top the spring 7 pulls it inward with such force that it slides inward and upward, abutting against the so stop block, thus effectually cutting out the shunt electro-magnets. Reference to the diagrammatic view Fig. 3 will make it clear how the shunt electro-magnets are cut out of the circuit. If this were not done a current wvould continue to pass through said shunt magnets after the carbons had stopped burning, and thus with many lamps in use a considerable loss would be incurred, all of which is saved by my invention. When the rack bar is elevated again the switch lever makes contact automatically with the rack bar, so that when the lamp is in condition to be started again no adjustment of said switch lever is necessary.

Having thus described my invention, what I claim, and desire to secure by Letters Patout, is-

1. In an arc lamp the combination with the rack bar provided with an insulating block, of the shunt electro-magnets, and a switch lever held in contact with said rack bar, and electrically connected with the shunt electromagnets, substantially as described.

2. In an arc lamp the combination with the rack bar provided with an insulating block having an inclined surface, of the shunt electro-magnets,a switch lever loosely pivoted and electrica ly connected with the shunt electromagnets, and a spring for holding said switch lever in contact with said rack bar, substantially as described.

Signed at New York, in the county of New York and State of New York, this 2d day of February, A. D. 1893.

JOHN THOMAS DEMPSTER.

Witnesses:

JOHN T. BEsWIoK, FRED. WILKIE. 

